One known method of making porous sintered nickel plates starts with a mixture comprising nickel powder, water, a plasticizer such as polyethylene glycol, and a processing agent which is preferably polyvinyl alcohol.
Such a method is described, for example, in U.S. Pat. No. 3,186,871.
After air has been added to the mixture to make it foam, the mixture is shaped and then heated, thereby drying it and sintering it and at the same time eliminating the plasticizer and the processing agent.
Nonetheless, various drawbacks have been observed with this process, in that the more or less foamy structure of the mixture collapses during heating thereby reducing its degree of porosity and leading to a substantially void-free structure inside the sintered material.
Porous metal bodies can also be made from metal-impregnated organic foams, e.g. polyurethane foam, which is subsequently heated. Such metallized foams can be prepared by mixing monomers with metal particles, and then triggering both the foaming and the solidification of the resin. Such a method is described, for example, in French Patent Specification No. 1 573 863. The large proportion of organic matter in comparison with the metal component in the resulting foam is a major source of drawbacks.
The elimination of organic matter during heating is a source of trouble and, in particular, the resulting high degree of shrinkage is a factor which tends to reduce porosity and which also often leads to cracking.
Preferred implementations of the present invention enable the above-mentioned drawbacks to be reduced. In particular, the method of the present invention can be used to produce a porous metal body with a predetermined pore fineness lying in the range 7 to 100 microns maximum, and this can be done starting from any of the commercially available powders. Furthermore, the method is reliable and easy to perform.